1. Field of the Invention
Exemplary aspects of the present disclosure generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a digital multi-functional system including a combination thereof, and more particularly, to an optical scanner that allows specification changes using common parts and an image forming apparatus including the optical scanner.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile capabilities, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member (which may, for example, be a photoconductive drum); an optical scanner projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
Known optical scanners for writing an electrostatic latent image on the surface of the image bearing member include a rotary polygon mirror that deflects and scans a light beam along the main scanning direction of the photosensitive drum.
Such optical scanners include a light source such as a semiconductor laser or the like, a coupling lens, an aperture, a cylindrical lens disposed on a light path between the light source and the rotary polygon mirror, a group of scan lenses including an f-theta lens and a face tangle error correction lens, and mirrors disposed between the scan lens and the photosensitive drum. The group of scan lenses is disposed between the rotary polygon mirror and a scanned surface of the photosensitive drum.
In recent years, there is growing market demand for production of images of ever-higher quality at ever-higher speeds. In order to accommodate such demand, a rotation speed of the rotary polygon mirror is increased from an original standard specification as needed, and the number of semiconductor lasers is increased to form multiple light beams.
When changes are made to the standard specification, configurations of devices need to be also changed to accommodate the changes. More specifically, when increasing the printing speed, an optical unit including multiple semiconductor lasers and a rotary polygon mirror with a higher rotation speed, or a whole new optical scanner is manufactured in addition to the standard devices so that depending on the specification changes, more appropriate devices can be installed in the image forming apparatus.
However, as is obvious, manufacturing a new optical unit and an optical scanner in addition to the standard devices increases manufacturing cost.
In view of the above, for changes in the rotation speed of rotary polygon mirror in particular, the rotary polygon mirror which is normally disposed on a drive circuit board is disposed separately from the drive circuit board, such as in JP-2006-326901-A. Instead, the rotary polygon mirror is attached to a different board (also called dummy board), and the drive circuit board is disposed outside an optical housing enclosing various optical components.
In this configuration, heat generated due to high-speed rotation of the rotary polygon mirror does not adversely affect the drive circuit board and components disposed thereon. Furthermore, the optical housing includes a plurality of circuit board mounts so that when the rotary polygon mirror rotating at higher speed is employed, the drive circuit board can be mounted at a different position to prevent the heat of the rotary polygon mirror from affecting the circuit board.
Although advantageous, in order to achieve high-speed scan with a single beam, a deflector such as the rotary polygon mirror needs to rotate at ever higher speed. Such a deflector capable of rotating fast is generally expensive and generates noise when rotating. Thus, a sound proof shield or the like to reduce noise is required, thus hindering efforts to provide the low-cost image forming apparatuses for which there is market demand.
In view of the above, there is thus demand for an optical writing device capable of accommodating changes from a standard specification without manufacturing new devices.